Conventional mechanical punch presses transmit the rotation of a flywheel rotating at a fixed speed to a crank system via a clutch brake thus converting this to a up-down movement of a ram. The speed cannot be changed mid-stroke.
From the point of noise reduction and high speed punching, a control that changes the speed mid-stroke is desirable. In short, the noise during punch processing is reduced if the speed when the punch tool strikes the workpiece is slowed down. However, a reduction in stroke speed causes a delay in the cycle timing of the punch processing. As a result, it is desirable to have a control that slows the speed when the punch tool actually strikes the workpiece mid-stroke and raises the stroke speed at other times.
This kind of punch speed control has been realised in general by a hydraulic punch press but the cost is increased due to the hydraulics. Even with a mechanical punch press, punch speed control is possible if driven by a servomotor. However, torque by the rotation of a servomotor is insufficient for obtaining a direct punch force.
The present applicant previously developed a punch press driven by a servomotor via a toggle system and also realised a mid-stroke speed change control on a mechanical punch press. On this punch press, the rotation speed of the servomotor reduces via a reduction gear the revolution count by, for example a tenth, and transmits the drive to the toggle system.
Moreover, according to this punch press, not only mid-stroke speed control but by using a revolution count which is widely changeable with a large output from the servomotor, everything from high speed processing of a large number of holes such as with nibbling processing to large hole processing having a large load can be realised by controlling the servomotor revolution count.
However, as the aforementioned servomotors with a large output and a wide range for changing the revolution count become extremely high quality, using them also greatly increases the cost. If a general servomotor has the specifications applicable to high speed processing, heavy load punch processing such as when the plate is thick, when large diameter holes are to be processed or when the material is hard, becomes impossible due to insufficient tonnage.
Conversely, if the servomotor has specifications for heavy load processing, high speed punching becomes unachievable. This kind of problem is not only limited to punch presses and occurs on other types of press machines.